Optimization and evaluation of reference region variable flip angle (RR-VFA) B1+ and T1 Mapping in the Prostate at 3T

Abstract

Purpose: To optimize and evaluate the reference region variable flip angle (RR-VFA) technique for simultaneous B+1 and T1 mapping of the prostate at 3 Tesla (T). Materials and Methods: The fat region surrounding the prostate was first identified using a fractional fat segmentation constant (tF) and a signal fat-fraction threshold (rF), and the relative flip angle (FA) was characterized using an effective fat T1 (T1f) within the fat region. Optimal values of tF, rF, and T1f were chosen by comparing relative FA maps using RR-VFA (ARR-VFA) with a reference relative FA maps (AREF) in the surrounding fat and evaluating interpolation errors within the prostate. The optimized RR-VFA was evaluated in volunteers at 3T on a single scanner (n = 10) and across three scanners (n = 4). Results: tF, rF and T1f were optimized as 0.5, 90%, and 320 ms, respectively. Prostate ARR-VFA showed differences of 30% among volunteers on one scanner, with no significant differences between ARR-VFA and AREF (P = 0.41). Prostate T1 after B+1 correction was 1998 ± 113 ms with significantly (P = 0.004) lower standard deviation than T1 before B+1 correction. The average coefficient of variation of prostate T1 across multiple scanners decreased from 15% to 5% after B+1 correction. Conclusion: The optimized RR-VFA can simultaneously measure B+1 and T1 in the prostate without the need for an additional scan and improve T1 consistency within and across MRI scanners at 3T. Level of Evidence: 3. J. Magn. Reson. Imaging 2017;45:751–760.